Bacterial endotoxins (LPS) are a major component of the outer membrane of Gram negative bacteria and mediate many of the pathophysiologic sequelae of Gram negative bacteremia. The interaction of LPS and host defense systems is mediated by a variety in vitro, macrophages are most sensitive to perturbation by LPS. Less than 100pg/ml of purified LPS will stimulate macrophage metabolism and secretion. We have demonstrated that certain salic acid containing glycosphingolipids (gangliosides) have the ability to inhibit LPS induced stimulation of both lymphocytes and macrophages. This inhibition may take place because of an interaction of ganglioside and LPS or by an alteration in the fluid properties of the plasma membrane of the responding cells by gangliosides. We have designed experiments to elucidate the role that gangliosides play in modulating macrophage responses to challenge with LPS and to examine the direct interactions of LPS and isolated gangliosides. Gangliosides are ubiquitous components of plasma membranes, including both lymphocyte and macrophages. Experimental evidence suggests an inhibitory role for these molecules with respect both B and T lymphocyte proliferation. The best defined functions for gangliosides have been as receptors for bacterial toxins, peptide hormones, and interferon. We have established procedures to produce large quantities of highly purified gangliosides from mouse and human tissue. These isolated gangliosides will be used to modulate the effects of LPS on cells of the macrophage-monocyte series. Macrophage glucose metabolism, enzyme secretion, and phagocytic ability will be assayed as they are affected by gangliosides in the presence and absence of LPS. The effects of gangliosides on oxidative metabolism of macrophages will also be measured. The molecular interaction of gangliosides and LPS will be dtermined by assaying binding of these two components in a liposome system. Large unilamellar liposomes will be prepared containing ganglioside species and the binding of LPS to each ganglioside will be measured as a model system for endotoxin receptors in plasma membranes. These experiments will further define the molecular basis of LPS-induced cellular responses as the relate to immunoregulation and pathophysiology.